1. Field of the Invention
The present invention relates to a thin film transistor and a method for fabricating the same, more particularly, to a thin film transistor for preventing short of circuit due to step and a method for fabricating the same.
2. Description of Related Art
Recently, thickness of gate insulation layer of a thin film transistor is gradually reduced. However, frequency of short generation between activation layer and gate electrode is increased as thickness of the gate insulation layer on the side wall of the activation layer is being reduced due to a high step generated as buffer layer in the lower part of the activation layer is etched at the same when the activation layer is formed.
The earlier art is described in detail as follows.
A polysilicon layer is formed by crystallizing an amorphous silicon layer deposited on a glass substrate equipped with buffer layer. Then, an activation layer is formed by patterning the polysilicon layer, and surface treatment process is performed using HF, etc., to remove impurities on the surface of the activation layer.
Next, a gate insulation layer is deposited on the substrate, and a gate electrode is formed on the gate insulation layer.
A step A1 is formed on the buffer layer accordingly since the buffer layer is over-etched in patterning process for forming the activation layer and surface treatment process for treating the surface of the activation layer.
It can be seen that thickness of the gate insulation layer on the side wall of the activation layer is reduced by the high step A1 formed by over-etching of the buffer layer. That is, it can be seen that thickness of the gate insulation layer on the side wall of the activation layer is reduced from B1 to B2. Therefore, a short can be generated between the activation layer and gate electrode as thickness of the gate insulation layer is reduced.
There is a method for forming the gate insulation layer thickly in order to solve the foregoing problems. However, there are problems in that driving voltage is increased, and power consumption is increased if the gate insulation layer is deposited thickly.